Search

In this study, the Zn-0.8Mg-0.28CaO wt.% composite was successfully prepared using different conditions of ball milling (rotations and time) followed by a direct extrusion process. These materials were characterized from the point of view of microstructure and compressive properties, and the correlation between those characteristics was found. Microstructures of individual materials possessed differences in grain size, where the grain size decreased with the intensified conditions (milling speed and time). However, the mutual relation between grain size and compressive strength was not linear. This was caused by the effect of other factors, such as texture, intermetallic phases, and pores. Material texture affects the mechanical properties by a different activity ratio between basal and pyramidal slips. The properties of intermetallic particles and pores were determined in material volume using micro-computed tomography (µCT), enhancing the precision of our assumptions compared with commonly applied methods. Based on that, and the analysis after the compressive tests, we were able to determine the influence of aspect ratio, feret diameters, and volume content of intermetallic phases and pores on mechanical behavior. The influence of the aspects on mechanical behavior is described and discussed. [ABSTRACT FROM AUTHOR]

Research on biodegradable iron-based materials has been increasing because they appear suitable for fabrication of temporary orthopedic and cardiovascular implants. Preliminary in vitro and in vivo studies have found that iron and some of its alloys exhibit good cyto- and biocompatibility. The main disadvantage of pure iron is its insufficient corrosion rate in physiological environments; therefore, it is necessary to modify it by suitable alloying. In this study, iron alloys containing 2 wt % of palladium, silver or carbon were prepared using powder metallurgy. The microstructure, mechanical and corrosion properties in a simulated body fluid were characterized. Compared to pure iron, alloying slightly increased porosity (from 15% to ∼ 18%) and decreased the compressive modulus of elasticity (from 5.6 to 1.1–1.8 GPa), compressive proof strength (from 145 to 113–127 MPa) and the Vickers hardness (from 63 to 23–37). Alloying with palladium and carbon enhanced (whereas silver lowered) the corrosion rate of iron in a simulated body fluid. Based on the obtained results, carbon and especially palladium appear to be suitable alloying elements for iron-based biodegradable materials. [ABSTRACT FROM AUTHOR]

Research into biodegradable porous materials has been increasingly focused on iron-based materials because such materials possess suitable properties for orthopedic applications. In this study, we prepared porous iron with porosities of 32-82 vol.% by powder metallurgy using ammonium bicarbonate as a space-holder material. We studied the influence of initial powder size and compacting pressure on sample microstructure, contamination and mechanical characteristics. The experimental results were analyzed as well, using Gibson-Ashby model and this analysis showed a good agreement in theoretical and experimental data. Whereas increasing compression pressure decreased porosity, the use of finer iron powder led to an increase in porosity. Increasing the amount of space-holder material in the initial mixture increased the total porosity, improved compressibility and consequently decreased the number of pores originating from imperfect compaction. A higher compacting pressure and the use of finer powder enhanced both the flexural and compressive properties. Even the most porous samples prepared from the fine iron powder possessed mechanical properties comparable to human cancellous bone. Based on these results, we can claim that the use of fine initial iron powder is necessary to obtain highly porous iron, which appears to be suitable for orthopedic applications. [ABSTRACT FROM AUTHOR]

The demand for porous biodegradable load-bearing implants has been increasing recently. Based on investigations of biodegradable stents, porous iron may be a suitable material for such applications. In this study, we prepared porous iron samples with porosities of 34–51 vol.% by powder metallurgy using ammonium bicarbonate as a space-holder material. We studied sample microstructure (SEM-EDX and XRD), flexural and compressive behaviors (universal loading machine) and hardness HV5 (hardness tester) of the prepared samples. Sample porosity increased with the amount of spacer in the initial mixtures. Only the pore surfaces had insignificant oxidation and no other contamination was observed. Increasing porosity decreased the mechanical properties of the samples; although, the properties were still comparable with human bone and higher than those of porous non-metallic biomaterials and porous magnesium prepared in a similar way. Based on these results, powder metallurgy appears to be a suitable method for the preparation of porous iron for orthopedic applications. [ABSTRACT FROM AUTHOR]

Abstract: There has recently been an increased demand for porous magnesium materials in many applications, especially in the medical field. Powder metallurgy appears to be a promising approach for the preparation of such materials. Many works have dealt with the preparation of porous magnesium; however, the effect of sintering conditions on material properties has rarely been investigated. In this work, we investigated porous magnesium samples that were prepared by powder metallurgy using ammonium bicarbonate spacer particles. The effects of the purity of the argon atmosphere and sintering time on the microstructure (SEM, EDX and XRD) and mechanical behaviour (universal loading machine and Vickers hardness tester) of porous magnesium were studied. The porosities of the prepared samples ranged from 24 to 29 vol.% depending on the sintering conditions. The purity of atmosphere played a significant role when the sintering time exceeded 6h. Under a gettered argon atmosphere, a prolonged sintering time enhanced diffusion connections between magnesium particles and improved the mechanical properties of the samples, whereas under a technical argon atmosphere, oxidation at the particle surfaces caused deterioration in the mechanical properties of the samples. These results suggest that a refined atmosphere is required to improve the mechanical properties of porous magnesium. [Copyright &y& Elsevier]

Abstract: Porous magnesium-based materials are biodegradable and promising for use in orthopaedic applications, but their applications are hampered by their difficult fabrication. This work reports the preparation of porous magnesium materials by a powder metallurgy technique using ammonium bicarbonate as spacer particles. The porosity of the materials depended on the amount of ammonium bicarbonate and was found to have strong negative effects on flexural strength and corrosion behaviour. However, the flexural strength of materials with porosities of up to 28vol.% was higher than the flexural strength of non-metallic biomaterials and comparable with that of natural bone. [Copyright &y& Elsevier]

Zinc-based alloys represent one of the most highly developed areas regarding biodegradable materials. Despite this, some general deficiencies such as cytotoxicity and poor mechanical properties (especially elongation), are not properly solved. In this work, a Zn-5Mg (5 wt.% Mg) composite material with tailored mechanical and superior corrosion properties is prepared by powder metallurgy techniques. Pure Zn and Mg are mixed and subsequently compacted by extrusion at 200 °C and an extrusion ratio of 10. The final product possesses appropriate mechanical properties (tensile yield strength = 148 MPa, ultimate tensile strength = 183 MPa, and elongation = 16%) and decreased by four times the release of Zn in the initial stage of degradation compared to pure Zn, which can highly decrease cytotoxicity effects and therefore positively affect the initial stage of the healing process. [ABSTRACT FROM AUTHOR]

In this work, the formation of intermetallics in Ni–Ti system by reactive sintering at 500 and 650 °C was studied. Mechanism and kinetics of the reactions leading to Ni–Ti phases were determined by DTA and the application of an experimental model consisted of nickel-plated titanium. It was found that Ti 2 Ni phase forms already at 500 °C. At 650 °C this phase undergoes a reaction with nickel to NiTi and Ni 3 Ti. The reactions were determined to be diffusion-controlled. The formation of Ni 3 Ti contributes to the porosity evolution during reactive sintering production of NiTi alloy. [ABSTRACT FROM AUTHOR]